1. Field of the Invention
Circuit arrangement and selected memory records allow locating the cause of a fault in the recording medium side or in the equipment side in a mass-storage system.
2. Description of the Prior Art
Generally, a magnetic disk pack unit is composed of a disk pack, which can be mounted or removed easily, and a main unit providing magnetic heads for reading or writing data from/to said disk pack, a modulator and demodulator, etc. If a fault occurs in such a magnetic disk pack unit, it is desirable to determine whether the fault lies in the main unit or in the disk pack. Various fault location methods are known.
The typical magnetic disk pack comprises plural magnetic disks piled with their center aligned in common, and both sides of each disk are used for magnetic recording.
Each recording medium surface generally includes plural cylindrical recording tracks and, for example, a series of cylinder addresses may be assigned in sequence from the inner to the outermost track. In addition, each recording medium surface is given a corresponding track address. Here, a "track" is used to specify one side of one magnetic disk, thus a recording medium surface, while a "recording track" specifies a cylindrical area within a recording medium surface or track. The reason why each recording medium surface is called a "track" is that it is an area to/from which data is written or read by only one head, which, as will be explained later, is analogous to a magnetic drum unit.
Each track (that is, each recording medium surface) is also divided into several "sectors". Therefore, each unit recording area is designated by a track address, a cylinder address and a sector address. This unit area is called a record. In a predetermined record in each recording track (cylindrical area) is stored the home address data of that recording track, and this home address data includes the track and cylinder addresses of the recording track itself.
The main unit of the magnetic disk pack provides a read/write head corresponding to each track, and all of these heads are arranged to move simultaneously as a single integrated assembly in the radial direction of the mounted disks. Also provided is the head selection circuit which selects only the head corresponding to a track address specified by a highly-ranked unit of the equipment, and the circuit connects the selected head to a modem.
A read/write operation for the record designated by the highly-ranked unit is performed as follows. First, the corresponding head is selected in accordance with the track address and the head moves from the outer recording track toward the inner tracks. The number of recording tracks which the head crosses are counted, and when the count equals the cylinder or recording track address value the head stops. The home address then passes below the head which is stopped at the addressed cylinder position, and the head reads out the track and cylinder addresses stored in the home address area. These are compared with the values specified by the highly-ranked unit for confirmation that they match. Then, for diagnostic purposes, either data that is stored in a predetermined sector address is subsequently read out after the home address data is sent to the highly-ranked unit, or data sent from the highly-ranked unit is written into a specified record.
A known method for fault location in such a unit is as follows.
First, record areas for diagnostic operation are provided on several tracks of the disk pack and the location of such diagnostic areas (track address, cylinder address, sector address) are recorded in a diagnostic area location record, for example, in the first sector of the first cylinder of the first track, which record might have the address of "0, 0, 0".
If a fault occurs (parity error, for example) during a read/write operation at a certain record, the read/write operation is generally attempted a second time after the disk makes a turn. If a fault occurs again the "0, 0, 0" record above is accessed to read out the addresses of the diagnostic areas.
If this read operation is performed successfully, then it is apparent that at least the demodulator circuit for the read operation is operative. Then, access is had to the first of the diagnostic areas according to the addresses read from the "0, 0, 0" record, and then some type of predetermined data is written there. Thereafter such data is read after the disk makes a turn and the data read out is compared with the data intended to be written, for confirmation. If these write and read operations are successfully performed, then it has been confirmed that the read/write circuits are operative. Further, proper operation of the head selection circuit can be examined by subsequently attempting similar write and read operations with the other diagnostic areas in other tracks. Thus, when normal operation of the entire main unit is confirmed, the cause of the fault can be assigned to the disk pack.
However, such known fault location methods have the following serious defect. Namely, a fault in a head cannot always be detected, if the cause of the fault lies in the head currently in use. In this case, a diagnostic area in the recording track corresponding to the defective head may not be properly written in the above-mentioned fault locating operation. Even if such a diagnostic test area is prepared in the relevant track, these tests are usually not performed in more than three tracks, so that defects in other heads may not be determinable. Thus, the diagnostic operation may be performed with different heads than the one in use when a fault is first detected. Thus, a defect in a head may not be detected. If diagnostic areas are provided in all the tracks and the write/read operations are attempted for all the heads when a fault occurs, a fault in a head can be detected. But, a longer diagnostic time is required and this method is not practical because of this disadvantage.